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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
   <script>
    // console.log(a)
    // let a = '123'
    // let a= 123;
    // console.log(a)
  

//    if(true){

    // var b = 123

//    }console.log(b)

//    if(true){

    // let c = 123

//    }
//    console.log(c)

   //   let 存在块级作用域，花括号即为作用域

   //  暂时性死区

   //const
    
    const a = 123;
    //  a= 20;
    console.log(a)
    const obj={name:'张三'}
    console.log(obj.name='李四')
    console.log(obj)
    const c;
    // const声名的变量不允许修改地址，可以修改值

</script>
</html>